Method of making a wheel cylinder assembly



R. L. SHELLHAUSE ET AL April 4, 1967 METHOD OF MAKING A WHEEL CYLINDER ASSEMBLY Original Filed Nov 19, 1962 I6 IO .2 1 24 2o 1 60 5a 22 0 44 :i L\

36 as y 46 INVENTORS Rona/d L. S/re(/hause BY Carl ,4. Bier/em Fig. 3

02x9 MW The/r Afforney United States Patent OfiFice Patented Apr. 4, i967 3,331,97ii METHUD F MAKll lG A WHEEL CYLHNDEE Ronald L. Shellhause, Vandalia, and Carl A. Eiierlcin,

Kettering, @hio, assignors to General Motors Cor tion, Detroit, Mich, a corporation of Delaware Original application Nov. it), 11962, Ser. No. 2353,5tl3, new Patent No. 3,187,848, dated .inne 8, 1965. Divided and this application 19, 54, Ser. No. 353,148

7 Claims. (Cl. 29-451) This is a division of our copending application Ser. No. 238,503, entitled, Wheel Cylinder Assembly and Method of Manufacture, and filed Nov. 19, 1-962, now US. Patent No. 3,187,848.

The invention relates to the method utilized in assembling the Wheel cylinder which is the subject of the above noted application. It more particularly relates to the assembly of a wheel cylinder of a type utilized in a wheel brake, the wheel cylinder assembly being so constructed that the wheel cylinder boot is received internally of the end of the wheel cylinder and is held therein by friction and cohesive forces and mechanical locking engagement obtained by fiowin the wheel cylinder boot material into the engaged surface of the wheel cylinder. A wheel cylinder assembly having this construction is advantageous in that it virtually elim'mates damage to the wheel cylinder boot during various handling operations prior to being asembled in a wheel brake, and provides for better radiant heat dissipation while the brakes are operating. Assemblies embodying the invention also provide better wheel cylinder boot retention characteristics which increase within a few hours after installation and further increase after a short period of use under normal operating conditions. The boot retention and link pin sealing characteristics are such that the boot link pin sealing section flips outwardly should an abnormal gas or fluid buildup occur behind the boot and within the wheel cylinder. This flipping action functions as a safety valve which will allow only a small fluid loss rather than a complete fluid loss should the entire boot be forced away from the wheel cylinder. The sealing section will continue to have a sealing action in the flipped condition. The internal position of the wheel cylinder boot also permits better heat dissipation characteristics by exposing the entire outer surface of the wheel cylinder to radiant heat being radiated from the brake shoes during the braking operation instead of having the wheel cylinder boot covering the cylinder end and thereby acting as a radiant heat insulator in this area and at the same time abosrbing more heat than its does when inside the cylinder.

In the drawing:

FIGURE 1 is a view of a portion of a wheel brake assembly embodying the invention and having parts broken away and in section.

FIGURE 2 is a perspective view of a wheel cylinder and boot in position just prior to installation of the boot in the cylinder, with parts broken away and in section.

FIGURE 3 is an enlarged partial view having parts broken away and in section and showing somewhat schematically the wheel cylinder boot as retained in the end of the wheel cylinder.

The wheel brake assembly may be of any suitable type and is illustrated in this instance as one the duo' servo type. It includes a drum in which is rotatable and to which the wheel is attached. A backing plate 12 is suitably attached to the vehicle. An anchor pin in is secured to the backing plate to receive and transmit the braking forces from the shoes 16 and lid to the vehicle through the backing plate. Shoes 116 and lid are movably mounted on the backing plate in the usual manner so that they are movable into and out of braking engagement with the drum it Suitable retractor springs 20 and 22 are secured to the anchor pin 14 in the usual manner so that they perform their usual functions, including retention of the guide plate 24 in place on the anchor pin.

The wheel cylinder assembly 26 is secured to the backing plate 121 in force-transmitting and heat conducting relationship in any suitable manner. The particular wheel cylinder assembly illustrated includes a cylinder body 28 in which a cylinder bore 30 is formed. Bore lid is smooth finished by suitable operations such as honing, as is well known to those skilled in the art. Cnly one half of the interior of the wheel cylinder assembly 2% is illustrated in section since the other end of the assembly is substantially identical thereto but in reverse relation. The invention is also applicable to wheel cylinders of other constructions than those required for duo-servo brakes.

A piston 32 is operably received in the bore 3i) and a cup seal 34 engages the inner surface of the piston and is retained in position against the piston by spring seat 36 and spring 35. Piston 32 is suitably recessed as at 4% to receive link pin 42 so that the link pin end 44 remains substantially on the center line of the wheel cylinder. Link pin 42 extends out of the wheel cylinder so that its other end as engages the web 4-? of shoe 18 in force transmitting relation. This portion of the structure is conventional except for the ends of the cylinder body 28, one of which is described below with regard to the wheel cylinder boot.

The wheel cylinder 5b is inserted in the end 52 of the cylinder body 28 and is provided with an annular inner seal section which is in sealing engagement with the link pin 42. Boot Ed is preferably constructed somewhat iii-1e half of a hollow torus so that the intermediate body section an extends from the inner seal section 54 first axially in one direction relative to the axis of the cylinder body and then curves as the radius increases until it extends axially in the other direction adjacent the outer peripheral section 58 of the boot. The outer peripheral section 55'; is preferably radially outward. of the inner seal section 54 and is formed as an annular cylindrical section having an outer surface as, an inner surface 62 and an end surface 64. The wheel cylinder boot is made of any suitable flexible material such as rubber, neoprene, styrene butadiene, or any elastomeric material having similar characteristics. Any material used must not be adversely affected by the hydraulic brake fluid utilized. it must also be able to Withstand temperatures in the area of 300 F. to 450 F. without melting, cracking or otherwise failing. It must be sufficiently flexible to permit the inner seal section 5'4 to move with pivotal movement of link pin 4-2 and to flip outwardly under excess pressure within the wheel cylinder body exteriorly of piston 32 without being permanently damaged. It must also be sufficiently strong to resist this flipping action until such excess pressures are obtained. This, of course, is a function of the physical proportions of the boot, taking into consideration the other physical characteristics of the material utilized.

The boot 5i) is preferably provided with a retainer ring as which can be bondedto the inner surface 62, or may otherwise be secured thereto. If desired the inner surface e2 may be the bottom of a shallow recess which has approximately the thickness of the retainer ring 66 so that the retainer ring is positioned against a boot shoulder 63 and its edge 7d is substantially in alignment with the end surface 6 of the boot.

The recess 72 formed in the end 52 of the wheel cylinder preferably has a greater diameter than the bore 3% so that a shoulder 74 is provided. The surface 76, which is the bottom of the recess 72, has a controlled finish which is provided with a predetermined roughness.

Where the finish of bore 30 is honed to approximately a micro-inches R.M.S. finish, surface 76 is finished so that it has a 60 to 120 micro-inches R.M.S. finish. This range is given here as indicative of the roughness but is not so critical that the roughness must be maintained within these exact limits. It has been found, however, that these limits yield satisfactory results without requiring the close control in the finish operation which is required in finish bore 30. The illustration in FI URE 3 indicating the roughness of this surface is for illustrative purposes only and is not indicative of the precise roughness desired.

The wheel cylinder boot Stl is installed in the recess 72 by pressing it axially inward. A lubricant such as diacetone alcohol or a glycol ether such as commercially available brake fluid may be used. The lubricant must assist in the installation without being so slippery that the immediate friction and cohesive interaction of the wheel cylinder body and the boot is insufficient to resist the outward force exerted on the boot by spring 33 through cup 36 and piston 32. Also, the lubricant must be compatible with the material of which the boot is made. Since the boot outer cylindrical surface 66 is preferably provided with a diameter so that it is a slight interfer ence fit in recess 72, the material of which the boot is made is slightly compressed upon installation. The boot is pressed axially into the recess 72, and by way of example, in a /8 wheel cylinder the installation force has been found to be from 10 to pounds. The boot is held in place by frictional engagement of its surface es With the controlled finish surface 76 immediately upon installation, and this frictional engagement dependent to some extent on the force exerted radially outward due to the inteference fit. These forces are augmented by the relative stiffness of the retainer ring as which resists radial collapse of the Wheel boot and therefore exerts a reaction force radially outward against the wheel cylinder body tending to compress the boot section 58. It has been found that immediate removal of the boot 50 after such installation can be accomplished by exerting a removal force axially against the retainer ring 56 which is approximately half of the installation force. Thus at this time the removal force is only required to overcome the frictional force plus a slight cohesive action. However, if the boot is permitted to set for a time without further work being done on or by the assembly, a removal force approximately equal to the installation force is required. This has been found to be caused by the flow of the material of which the boot is made at and near surface 60 into the controlled roughness surface 76 so that these surfaces are mechanically locked. This is illustrated in FIGURE 3 in a non-scale presentation. This flow condition can be accelerated appreciably by exerting radial forces against the retainer ring 66 so as to cause the surface 60 of the boot to flow more quickly into complementary engagement with the controlled finish surface 76. This may also be accomplished by using the wheel cylinder at normal brake operating temperatures for a short period of time. It has been found for example that after such usage the removal force required is approximately double or triple the installation force. It is believed that this occurs due in part to a cohesive reaction between the cylinder and the boot. It may also be due in part to some pressures being exerted internally of the wheel cylinder boot in the chamber '78 formed by the boot, the piston 32, the link pin '42, and the cylinder body 28. These pressures are obtained by normal movement of the piston 32 in the bore .30 which alternately decreases and increases the volume of chamber 78. The heating of the wheel cylinder boot under operating conditions, as well as the heating of the cylinder body, also contributes to the full mechanical lock condition of the boot. Heat at or below the normal operating temperature range of the boot, and therefore ambient temperatures can therefore be used to accelerate the mechanical lock condition, or in conjunction with the radially outward forces noted above, or independently of them. It is well known that elastomer materials such as those of which boots may be made suffer a compression set when compressed for long periods of time. This set in the section 58 of the boot does not decrease the removal forces required after some months, for example. It is thought that this set is counteracted by the effectiveness of the cohesive and mechanical lock of the surfaces tiil and '76.

It has been found that at times the shoe web temperatures will be as high as 850 F. for short periods when the brakes are temporarily overloaded. The heat is radiated from the drum and the shoes to the backing plate, the Wheel cylinder, the retractor springs, and any other elements exposed to them in radiant heat relation. In previous commonly used wheel cylinder constructions the wheel cylinder boots were made sufiiciently large to be fitted tightly over the outside of the wheel cylinder ends. This construction is typical of all current production brakes of the duo-servo type. In this construction the ends of the wheel cylinder, which are the parts of the wheel cylinder bodies closest to the shoe webs, are insulated by the boots. Thus the wheel cylinder cannot function as a heat sink and heat transfer member wherein it receives the radiant heat from the shoes and transmits it to the backing plate. Instead the outer peripheries of the Wheel cylinder boots receive extreme amounts of radiant heat under extreme brake conditions and tend to hold it without transferring it. This causes them to crack and fail prematurely. This also results in less net heat removal from the brake shoes in a given unit of time, this contributing to the tendency of the brakes to fade since they reach and retain higher shoe temperatures at an earlier point in time. By use of the structure embodying the invention however, the entire outer surface of the wheel cylinder body 28 is exposed to radiant heat from the shoe webs and, commonly being made of cast iron, readily absorbs this heat and transmits it to the backing plate so that the boots are protected for an additional period of time. This also tends to decrease the fade tendency of the brakes since the heat is not retained as long as before. Also the wheel cylinder boot does not have its relative section exposed to the extremely high radiant temperature, but to a lesser temperature found in the wheel cylinder body ends, therefore decreasing the likelihood of failure of the boot. In the particular mechanism embodying the invention it is preferable to have all of the annular cylindrical outer peripheral section 58 of the boot shielded by the end of the wheel cylinder. Thus decreasing the radiant heat exposure of the boot to a minimum While permitting it to operate in the usual manner.

Another particularly important advantage of the invention is obtained after assembly of the wheel cylinder unit and during handling thereof. In prior construction units wherein the boot was put over the cylinder end, the boot would often be almost invariably cut. If the wheel cylinder was dropped from a height of approximately one foot to a solid surface such as a concrete floor, a work bench, or table, etc., this cut may be relatively minute in many instances but forms a weak spot where high stresses occur and becomes the direct cause of premature boot failure. By placing the boot inside the wheel cylinder end as contemplated in accordance with the invention, handling damage to the boot is eliminated. The wheel cylinder embodying the invention can be dropped from a height of five feet on most types of surfaces, including edges of machinery, benches, tables, etc., as well as concrete floors without damage to the unit. In particular no cuts occur on the boot. This is an extremely important advantage in the manufacture of wheel cylinder assemblies since such assemblies are handled by hand or machinery numerous'times after being put together, not

the least of which is the handling of replacement wheel cylinders by mechanics in all types of garages.

We claim:

11. The method of sealing the end of a wheel cylinder comprising the steps of providing a controlled roughness inner surface in the end of the wheel cylinder, inserting an elastomeric wheel cylinder boot therein into outer peripheral engagement with the controlled roughness inner surface under an insertion force within a first predetermined range, force removing the insertion force and subsequently flowing the material of the boot into complementary engagement with the controlled roughness surface of the wheel cylinder end to provide a mechanical lock therewith for retaining the boot in the cylinder end against a removal force substantially greater than the necessary insertion force.

2. The method of claim 1, further comprising the step of exerting a radially outward retaining force against the inner surface of the wheel cylinder boot whereby the boot material flow step is accelerated.

3. The method of claim 2, the radially outward force being applied by mechanical means permanently formed as a part of the boot.

4. The method of claim 2, the radially outward force being provided at least in part by a fluid pressure exerted on the inner surface of the wheel cylinder boot.

5. The method of claim 2, further comprising the step of heating the assembled wheel cylinder and wheel cylinder boot to accelerate material flow.

6. The method of claim 5, the heating step being obtained by initial operation of the wheel cylinder assembly under conditions whereby heat is generated through operation thereof.

7. The method of claim 5, the heating step being obtained by heating the wheel cylinder assembly above ambient temperature to a point below that which will cause damage to the material of the boot.

References Cited by the Examiner UNITED STATES PATENTS CHARLIE T. MOON, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,311,970

Ronald L. Shellhause et a1.

April 4, 1967 rs in the above numbered pat- It is hereby certified that error appea Letters Patent should read as ent requiring correction and that the said corrected below.

Column 1, line 64, after "one" insert of column 4,

line 58, for "be almost invariably" read be Signed and sealed this 7th day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. THE METHOD OF SEALING THE END OF A WHEEL CYLINDER COMPRISING THE STEPS OF PROVIDING A CONTROLLED ROUGHNESS INNER SURFACE IN THE END OF THE WHEEL CYLINDER, INSERTING AN ELASTOMERIC WHEEL CYLINDER BOOT THEREIN INTO OUTER PERIPHERAL ENGAGEMENT WITH THE CONTROLLED ROUGHNESS INNER SURFACE UNDER AN INSERTION FORCE WITHIN A FIRST PREDETERMINED RANGE, FORCE REMOVING THE INSERTION FORCE AND SUBSEQUENTLY FLOWING THE MATERIAL OF THE BOOT INTO COMPLEMENTARY ENGAGEMENT WITH THE CONTROLLED ROUGHNESS SURFACE OF THE WHEEL CYLINDER END TO PROVIDE A MECHANICAL 